This invention relates to a push-pull valve for gas sampling bags, which are used to collect samples of potentially toxic gas. Such bags may be used to capture gas samples at toxic waste sites, industrial stacks, or landfills, and may have medical applications as well.
Because the concentration of toxic gases in samples may be very low, the sampling bag has to be clean, and empty initially. It is important to prevent ambient air and other gases from entering the bag before the sample is taken, and even more important to prevent leakage of the sample from the bag.
A test procedure may require the taking of hundreds of samples, so it is important that filling a bag with a gas sample be a simple, quick operation. Valves are typically installed on such bags to permit the tester to open, fill, and then seal the bag. The valve must be reliable, and in addition, inexpensive, again because of the number of bags which must be used. In most cases, the valve and bag will be used only once before disposal.
Prior inventors have proposed valves having a hollow stem which can be pulled or pushed, rotated or hinged to either close or open the valve. Some such valves have been used on gas sampling bags.